1. Field of the Invention
This invention relates to improvements in and concerning a multi-flow type heat exchanger to be incorporated in an automobile air conditioner.
2. Description of the Prior Art
Among the heat exchanger recently proposed for use as in condensers of automobile air conditioners are included those of the multi-flow type which are configured as illustrated in FIG. 34 (as disclosed in U.S. Pat. No. 4,615,385 and Japanese Patent Application Disclosure SHO 62(1987)-175,588, for example).
The heat exchanger of this multi-flow type is provided with a pair of header pipes 1, 2 separated by a prescribed length e from each other and disposed parallelly to each other. An inlet tube 3 for introducing a heat-exchanger fluid such as a refrigerant is fitted to the inlet side header pipe 1 and an outlet tube 4 for discharging the heat-exchanger fluid is fitted to the other outlet side header pipe 2. Between the two header pipes 1, 2, a multiplicity of flat tubes 5 are installed so as to intercommunicate these two header pipes 1, 2. Thus, the heat-exchanger fluid flowing in through the inlet side header pipe 1 advances in the form of a plurality of parallel flows and flows into the outlet side header pipe 2. On the opposed side surfaces of the two header pipes 1, 2, bulged parts 6 of the shape of a dome are formed as illustrated in FIG. 35 for the purpose of enhancing the heat exchangers' strength to resist pressure.
In FIGS. 34 and 35, the reference numeral "7" denotes a corrugated fin for transfer of heat, the reference numerals "8 and 9" denote blank covers, and the reference numeral "10" denotes a reinforcing plate.
In the flat tube 5, an inner fin 11 whose cross section taken perpendicularly to the axis thereof is corrugated with a prescribed pitch p as illustrated in FIG. 36, is inserted and fixed in place. The inner fin 11 serves the purpose of partitioning the flow path r of the flat tube 5 and giving rise to a plurality of independent small flow paths 12 therein.
In this heat exchanger H of the multi-flow type, therefore, the heat-exchanger fluid which flows in the inlet side header pipe 1 advances collectively in the form of a plurality of parallel flows in the direction of the outlet side header pipe 2 and, at the same time, advances in the form of parallel flows severally inside the small flow paths 12.
The heat exchanger H of the multi-flow type, for the sake of enhancing the capacity thereof for exchange of heat, has the small flow paths 12 each so adapted that the equivalent diameter (the diameter of a flow path having a circular cross-sectional area equaling the cross-sectional area of the small flow path) thereof has a predescribed value. Specifically, in consideration of the pressure drop occurring in the flowing air, the resistance offered to the flow of the heat-exchanger fluid and the heat-exchange efficiency, the heat transfer area is adjusted to a prescribed value so as to heighten the whole heat exchange efficiency of the heat exchanger. There are heat exchangers which use the so-called serpenine tubes (flat tubes of an elliptical section extrusion molded so as to form a plurality of flow paths inside). The heat exchanger of the multi-flow type described above, as compared with the heat exchanger of the type using the serpentine tubes, has the merit high pressure-resisting capacity, small size, and light Weight ascribable to the formation of bulged parts 9 on the header pipes 1. 2 in addition to enjoying the advantages of small thickness of tube low resistance to the fluid in motion, and high capacity for exchange of heat.
The heat exchanger of the multi-flow type, however, is problematic in terms of performance and in terms of manufacture.
First as concerns the performance, the inner fin 11 is soldered in place within a furnace in such a manner as to define the flow paths 5 inside the flat tube 5 as illustrated in FIG. 36. The small flow paths 12 consequently formed herein extent straightly from the leading ends to the trailing ends thereof. The heat-exchanger fluid flows just straightly inside the flat tube 5 and has no possibility of being stirred while in motion therein. It is not inconceivable that the portion of the heat-exchanger fluid which flows along the central part of the cross section of the small flow paths 12 just advances through the interior of the flat tube 5. The heat-exchanger fluid does not wholly contribute to the action of exchange of heat.
The portions of the heat-exchanger fluid flowing inside the small flow paths 12 defined by the inner fin 11, while in motion between the header pipes 1, 2, are not intermingled with one another but simply advanced without being allowed to manifest the heat exchange ability to a sufficient extent.
In connection with this point, Japanese Patent Application Disclosure SHO 61(1986)-295,494 and Japanese Utility Model Application Disclosure SHO 62(1987)-39,182 disclose a corrugated inner fin so configured that the waves thereof are staggered by a prescribed pitch. This inner fin is capable of imparting a zigzagging flow to the heat-exchanger fluid and incapable of manifesting the heat exchange ability fully satisfactorily.
The heat exchanger of the multi-flow type is further problematic in terms of manufacture.
The inner fin 11 is soldered within the furnace in conjunction with all of the other component members of the heat exchanger including the flat tube 5. In this case, the step of applying flux to the ridge parts 11a of the inner fin 11 is required to precede the step of entering the component members of the heat exchanger in the furnace. In this step, however, since the inner fin 11 is corrugated as illustrated in FIG. 37, the flux adhering to the ridge parts 11a trickles down the sloped surfaces and collects in the groove parts 11b. As the result, the flux adheres in an insufficient amount to the surface of the ridge parts 11a which require the flux to be deposited most thickly and the work of soldering consequently becomes extremely difficult.
Further, the heat exchanger H of the multi-flow type, as disclosed in U.S. Pat. No. 4,651,816, is fixed in place by causing brackets 13 attached fast as by soldering to the header pipes 1, 2 to be bolted to the car body or to other heat exchanger such as, for example, the radiator in the engine cooling cycle. The brackets 13 are generally made of aluminum. After the mounting positions for the brackets which are variable with vehicles are corrected by the use of jigs, for example, the brackets are soldiered integrally within the heating furnace at the same time that the flat tubes 5 and the corrugated fins 7 are soldered or they are first soldered and then fixed in place as by the TIG welding.
Incidentally, when the fixation is effected by the work of soldering as described above, it is generally difficult to solder the brackets while maintaining the accuracy of the mounting positions. The TIG welding proves to be disadvantageous in terms of productivity and cost because the number of steps of process is large.
Japanese Utility Model Application Disclosure SHO 61(1986)-110,017 discloses a structure for fixing the heat exchanger in place without being welded. Since the heat exchanger in this disclosure has no use for the header pipes, the number of component parts is unduly large and the assembly of such component parts consumes much time and labor.